Alloying-jig for alloying contacts to semi-conductor bodies



March 12, 1963 D. ALLOYING-JIG FOR ALLOYING CONTACTS TO SEMI-CONDUCTORBODIES Filed July 19, 1960 DE NOBEL 3,080,841

BY E I hazel. j AGENT United States Patent Ofiice 3,080,841 PatentedMar. 12, 1963 3,080,841 ALLOYING-JIG FOR ALLOYING CONTACTS TOSEMI-CONDUCTOR BODIES Dirk de Nobel, Eindhoven, Netherlands, assignor toNorth American Philips Company, Inc., New York, N.Y., a corporation ofDelaware Filed July 19, 1960, Ser. No. 43,813 Claims priority,application Netherlands Aug. 25, 1959 3 Claims. (Cl. 113-99) Theinvention relates to an alloying-jig for alloying contacts tosemi-conductor bodies, in particular for the manufacture of transistors,crystal diodes, and similar semi-conductor electrode systems, and inaddition to a method of manufacturing such a jig. An alloying-jig is tobe understood to mean here apparatus or a device in which one or morespaces are recessed which may serve for receiving semi-conductor bodiesand in which in addition one or more apertures are available for fixingthe material for the contacts. Beforehand, this material has mostly beenshaped as pellets or wafers which may have a diameter of for example afew tenths of a millimeter. Alloying itself is carried out bytransferring the jig into an oven and then subjecting it to the requiredheat treatment.

The alloying-jigs are usually manufactured from graphite, because thismaterial can be prepared with a very high degree of purity and such apurity is an important factor in the relative branch of the technology.In addition, graphite is not wetted by the melted contact material.However, in comparison with the very small apertures which have to bemade in the jig, graphite is of coarse grain. Owing to the smallstrength of the graphite, the jig is highly subject to wear. Inaddition, graphite may easily absorb contaminating gases and vapours, so

Although molybdenum is rather hard, it is readily machinable with normalhard steel tools. However, molybdenum is wetted by melted contactmaterial. The invention is based on the further recognition thatmolybdenum can very well be coated with a refractory, non-metallic filmwhich is not wetted by molten contact material.

Such a film on molybdenum turned out to be readily resistant to varyingtemperature treatment to which jigs for alloying are usually exposed.The application of such a film on molybdenum has already been proposedfor corrosion resistant purposes; The invention is based on the furtherrecognition that on molybdenum a skin can be provided which, in contrastwith the corrosion resistant oxide film of stainless steel jigs, issubstantially not reduced by hydrogen.

The alloying-jig according to the invention consists at least partiallyof molybdenum the surface of which is at least partially provided with afilm of refractory, nonmetallic material which substantially cannot bereduced by hydrogen.

According to a preferred embodiment, the film has i been obtained byapplying a material with which the molybdenum of the base forms agenetic layer. A genetic layer is to be understood to mean herein alayer mainly consisting of a reaction product between one or morecompounds of the material of the base to which the of it adjoining themetal.

that the jig has to be annealed repeatedly when using it frequently.

It has already been suggested to manufacture alloyingjigs of stainlesssteel, in particular of chrome iron steel, which is coated with acorrosion resistant oxide film. Such jigs can be manufactured with ahigh degree of accuracy and are subject to only little wear. The oxidefilm prevents the steel from being wetted by the melted contactmaterial. It has appeared, however, that this oxide film may bepartially reduced in the hydrogen atmosphere used during alloying, sothat such a jig can be subjected only for a short time to a treatment atalloying temperatures, which, moreover may not be too high, the oxidefilm having to be regenerated practically after each alloying treatment.In addition, the coefiicient of linear expansion of most kinds ofstainless steel are larger than 10x10, which is much larger than thecoefiicients of expansion of the commonly used semi-conductor materials,such as germanium and silicon which amount to 6.1 l0- and 4.2 10-respectively. So the danger exists that during the cooling from thealloying temperature to room temperature the contacts applied may bepushed off by uneven shrinkage of the jig and the semiconductor body.

One of the objects of the invention is to supply a material for jigs foralloying which does not have the above draw-backs, is easy and accurateto machine, and has a coefficient of expansion differing only slightlyfrom that of the commonly used semi-conductor materials, such asgermanium and silicon.

The invention is based on the recognition that molybdenum would beextremely suitable for the above purposes. Its coefficient of linearexpansion amounts to approximately 5 10- and consequently differsslightly from that of germanium or silicon. In addition, molybdenum ishighly refractory and not readily deformable.

Preferably, the material to be applied for the formation of the film isdeposited from the gaseous phase, as a result of which very slight filmthicknesses can be obtained, so that in the mechanical processing of themolybdenum for shaping the jig the thickness of the film to be appliedneed not be taken into account. A suitable film may be formed forexample by depositing carbon. The film is preferably formed bydepositing silicon or silicon and carbon. Such films have turned out tobe very lasting.

It has appeared that such an alloying jig is very useful inter alia attemperatures above 700 C. for example up to 900 C. and higher, forexample 1100 C. in a hydrogenous atmosphere. As a result, the jig isparticularly suitable for use in alloying contacts to silicon bodies.However, its use is not restricted to this particular semiconductormaterial. It is also readily usable in alloying contacts to germaniumbodies and in particular renders a very accurate location of thecontacts and temperatures of at least 700 C. are possible, also duringthe long periods required for forming difiFusion layers underneath thealloying contacts. For such high temperatures and long heating times,the known stainless steel jig is not suitable.

Since the coefi'icient of linear expansion of molybdenum differs littlefrom that of semi-conductor materials, such as germanium or silicon, thejig may be used in particular for alloying several contacts distributedover a relatively large surface of for example a plate-like and/orstrip-like semi-conductor body without one or more of the contactsapplied being pushed off on cooling after alloying owing to shrinkage ofthe jig even if the largest distances between apertures for fixing thecontact material should amount to 1 cm. or more.

In order that the invention may be readily carried into effect, it willnow be described in greater detail by way of example with reference tothe accompanying drawing.

The FIGURE shows an alloying-jig on an exaggerated scale, partly invertical section, partly in perspective.

In the figure, 1 is a graphite plate with a recess 2 in which astrip-like semi-conductor body 3, for example,

of n-type or p-type silicon, is laid. On the plate 1 is a molybdenumplate 4 provided with a non-metallic surface film 5 of one of the abovedescribed kinds, which plate is provided with apertures6.

The inner walls of the apertures 6 are likewise coated with the surfacefilm 5. The apertures 6 contain pellets 7 of contact material. Forexample, they may be of aluminum, or lead antimony, or any of theWell-known contact materials for silicon. The assembly may betransferred to an oven in a normal manner, in which, for example at atemperature of 900 C. in a hydrogen atmosphere, the pellets 7 meltwithin the apertures 6 and alloy to the silicon body 3.

The alloying time may vary between 1 and 30 minutes.

It has appeared to be well possible to make apertures having a diameterof 100a and a mutual spacing of 50 1. also in a molybdenum plate of forexample 100-200 thick. Such dimensions can practically not be achievedwhen using graphite.

The surface film 5 may be applied in a known manner. For example, themolybdenum plate 4 provided with apertures was heated at .1000 C. and agas current, composed of 10 parts by volume of hydrogen and one part byvolume of a gas mixture consisting of hydrogen which was saturated atroom temperature with vapour of silicon tetrachloride, was passed alongthe plate for 10 minutes, after which the resulting layer was reannealedat a temperature of between 1250" C. and 1300 C. .for about 10 minutesin pure hydrogen.

Another film of good quality was obtained by first treating themolybdenum part in the above manner at 1000" C. with SiCh-vapour andhydrogen and then treating with a gas mixture consisting of 10 parts byvolume of hydrogen and 1 part by volume of butane for 5 minutes at thesame temperature after which the layer was reannealed in theabove-manner. With the resulting film, the jig turned out to be welluseful at a temperature of 1100 C.

Both processes are believed to produce a molybdenum silicide ordisilicide coating or plating on the molybdenum. The technique describedis sometime referred to as vapour-plating. Other suitable coatingsinclude 13 0, SiC, MOC, M 0, which similarly may be formed by avapour-plating process, which involves reducing or decomposing avolatile compound of the coating material upon the heated molybdenumbody or specimen, depositing an adherent coating of the non-volatilereaction products.

What is claimed is:

1. Apparatus for fusing contact material to impuritysensitivesemiconductive bodies in a hydrogen-containing atmosphere, comprisingsupport means for receiving and supporting a semiconductive wafer, and amember arranged generally parallel to and mounted on said support andhaving a surface-coated molybdenum portion overlying and contacting asurface of said wafer, said 1. member containing an aperture overlyingthe wafer surface for receiving and positioning a mass of contactmaterial in engagement with the wafer surface for melting Within saidaperture, said surface-coating on the molybdenum portion being anadherent non-metallic refractory surface film selected from the groupconsisting of molybdenum carbides, molybdenum silicides, siliconcarbides, and boron carbide, and which is not wetted by the moltencontact material and not substantially reduced by hydrogen.

2. Apparatus for fusing contact material to impuritysensitivesemiconductive bodies in a hydrogen-containing atmosphere, comprisingsupport means for receiving and supporting a semiconductive wafer, and athin plate arranged generally parallel to and mounted on said supportand having a surface-coated molybdenum portion overlying and contactinga surface of said wafer, said plate containing an aperture overlying thewafer surface for receiving and positioning a mass of contact materialin engagement with the wafer surface for melting within said aperture,said surface-coating on the molybdenum portion being an in-situ formedadherent non-metallic refractory surface film selected from the groupconsisting of molybdenum carbides, molybdenum silicides, siliconcarbides, and boron carbide, and which is not wetted by the moltencontact material and not substantially reduced by hydrogen.

3. Apparatus for fusing contact material to impuritysensitivesemiconductive bodies in a hydrogen-containing atmosphere, comprisingsupport means for receiving and supporting a semiconductive wafer, and amolybdenum plate arranged parallel to and mounted on said support andhaving a surface-coating and overlying and contacting a surface of saidwafer, said plate containing a pair of apertures spaced apart andoverlying the wafer surface for receiving and positioning a pair ofmasses of contact material in engagement with the wafer surface for melting within said apertures, said surface-coating on the molybdenum platebeing an in-situ formed adherent nonmetallic refractory surface filmselected from the group consisting of molybdenum carbides, molybdenumsilicides, silicon carbides, and boron carbide, and which is not wettedby the molten contact material and not substantially reduced byhydrogen.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Industrial Heating, Col. 22, 1955, pages 23522360 relied onBerg-U. Huttenmann, Monatsh. Hochschule Leoben, vol. 97, pages 81-91,1952.

1. APPARATUS FOR FUSING CONTACT MATERIAL TO IMPURITYSENSITIVESEMICONDUCTIVE BODIES IN A HYDROGEN-CONTAINING ATMOSPHERE, COMPRISINGSUPPORT MEANS FOR RECEIVING